Cadmium plating



Patented Oct. 25, 1949 CADMIUM PLATIN G Allan E. Chester, Highland Park,and Frederick F. Reisinger, Waukegan, Ill., assignors to Poor & Company,Chicago, 111., a corporation of Delaware No Drawing. Application July24, 1944, Serial No. 546,439

Claims.

This invention relates to the electrodeposition of cadmium, toelectrolytes therefor, and to compositions adapted to be incorporatedinto cadmium plating baths.

One of the objects of the invention is to provide new and improvedcadmium plating baths.

Another object of the invention is to provide new and improvedcyanide-cadmium plating baths containing complex organic compounds whichare soluble in the bath and which produce improved color and brighteningeffects.

An additional object of the invention is to provide a new and improvedmethod for electrodepositing bright cadmium plates. Other objects willappear hereinafter.

In accordance with the invention, it has been found that greatlyimproved results in cadmium plating from cyanide-cadmium baths areobtained by electrodepositing the cadmium from an electrolyte containingan amine salt of an aldonic acid and/or a nickel salt of an aldonicacid. The term amine salt of an aldonic acid is employed herein todescribe reaction products of amines with aldonic acids. In the practiceof the invention it is preferable to employ amine salts derived fromrelatively high molecular weight amines. The preferred type of aminesalt for the purpose of this invention is alpha naphthylamine gluconate.A preferred nickel salt for the purpose of the invention is nickelgluconate. It will be understood, however, that other types of aminesalts may be employed, and that other nickel aldonates may be used.

The invention will be further illustrated, but is not limited, by thefollowing example in which the proportions are given in parts by weightunless otherwise indicated:

Example (A) A mixture of Grams Alpha naphthylamine 20 and 50% gluconicacid 120 was refluxed for 2 hours and then allowed to cool. Theresultant reaction product herein referred to as alpha naphthylaminegluconate solidified on cooling.

(B) A nickel carbonate was prepared by dissolving 349 grams of singlenickel salts (NiSO4.7H20) in a gallon of boiling water, separatelydissolving 356 grams of sodium carbonate in a gallon of boiling water,and then mixing together the two solutions with vigorous stirring. Themixture was allowed to settle for a few minutes and the freshlyprecipitated nickel carbonate was filtered 01f. The precipitate waswashed several times with hot water until there was no more sulphate ionin the Wash water. The precipitate was then sucked dry and dissolved in970 grams of hot 50% gluconic acid. The resultant solution of nickelgluconate was then adjusted to 3 liters by the addition of water,thereby producing a solution containing 24 grams per liter of nickel.

(C) A cadmium electrolyte was prepared by dissolving 12 ounces of sodiumcyanide and 5 ounces of cadmium oxide in a gallon of water.

(D) A stock solution was prepared by mixing together the followingingredients:

2 grams of the alpha naphthylamine gluconate prepared as in (A) 14 cc.of the nickel gluconate solution prepared as in (B) 50 cc. of thecadmium electrolyte solution prepared as in (C) 50 cc, ofdiethyleneglycolmonobutylether.

When cadmium is electroplated from the electrolyte prepared as in (C), adull gray plate is obtained. However, if a small amount of the reactionproduct prepared as in (A) is added to this same electrolyte, aconsiderable brightening effect is produced. If (A) alone is used, asubstantial brightening effect is obtained with as little as 0.25 gramof (A) per gallon of electrolyte. Larger amounts may be employed,although there is little point in adding more than about 1 gram of (A)per gallon of electrolyte because an excess beyond this amount does notproduce a comparable improvement in result.

A considerable brightening effect is also obtained if a nickel gluconateprepared as in (B) is incorporated with the cadmium electrolyte (C) insmall amounts, preferably within the range of 0.25 gram to 1 gram pergallon of electrolyte.

The alpha napthylamine gluconate produced as in (A) and the nickelgluconate produced as in (B) are both soluble in the bath of the cadmiumelectrolyte produced as in (0). As previously indicated, each of thesesubstances alone, when added to the cadmium electrolyte (C), produces abrightening effect. In case each substance is added alone, however, theeffective range of current density which will produce good results inthe electrodeposition of cadmium is relatively narrow, being up to about40 amperes per square foot in case (A) alone is added, and up to about25 amperes per square foot in case (B) alone is added. On the otherhand, if both (A) and (B) are incorporated into the cadmium electrolyte,a remarkable brightening eifect is obtained and the bright range iscomplete for current densities up to 100 amperes per square foot.Excellent results are obtained with current densities between 20 and 100amperes per square foot, bright deposits being obtained without burningthe metal. Even higher current densities may be used with very goodresults.

The alpha napthylamine gluconate and the nickel gluconate are preferablyadded in the form of the composition described under (D). Ten to 15 cc.of composition (D) per gallon of electrolyte (the electrolyte beingsimilar to electrolyte will give a pronounced effect with respect toincreased brightness of the electrodeposited .cadmium, and brilliantdeposits are obtained with as little as 57 cc. of composition (D) pergallon of cadmium electrolyte. Electrolytes prepared in this manner arealso good barrel plating electrolytes.

In'a similar manner, other amine salts of aldonic acids may be employedwhich may be prepared as described in our co-pending application SerialNo. 546,438, filed of even date herewith. Amine salts of aldonic acidsformed from relatively high molecular weight amines, and particularlyarylamines, are preferred for the practice of the invention. Among saidsalts are those derived from alpha napthylamine and beta naphthylaminereacted with aldonic acids, such as for example gluconic acid, mannonicacid, galactonic acid, arabonic acid, and xylonic acid. All of thesealdonic acids exist in alpha and beta lactone forms. Theamine-gluconates are preferable for the practice of the inventionbecause gluconic acid is less expensive and more readily available thanthe other aldonic acids. These acids are usually obtained by theoxidation of aldoses and are ordinarily prepared in the form of aqueoussolutions.

Instead of nickel gluconate, other nickel salts of aldonic acids may beemployed, including nickel salts of any of the aldonic acids previouslymentioned. These are preferably prepared from freshly precipitatednickel carbonate in the mannerdescribed in the foregoing example.

It will be understood that the proportions of the amine salt of thealdonic acid and the proportions of the nickel salt of the aldonic acidmay be varied somewhat. In general, as previously indicated, relativelysmall amounts of the amine salt of the aldonic acid and of the nickelsalt of the aldonic acid, either alone or in combination, will produce apronounced brightening efiect. Larger amounts may be used but ordinarilyare not necessary to obtain the result, and therefore merely add to thecost of the operation. Thus, the amount of alpha napthylamine gluconateis preferably around 1 gram per gallon of cyanide-cadmium electrolyte,although a substantial brightening effect is obtained with as little as0.25 per gallon. The addition of larger amounts, however, is notordinarily justified by an increasing improvement in brightening effect.results with nickel gluconate, preferably when employed in combinationwith the alpha napthylamine gluconate, are obtained with about '7 cc.per gallon of electrolyte of the" nickel gluconate solution containingaround 24 grams per liter of nickel, but effective results can beobtained with as little as one-fifth of that amount.

As illustrated in the example, it is preferable to employ a watermiscible organic solvent in the Similarly, the ultimate preparation ofthe stock solution. Among the suitable solvents are butyl Carb'itol andmethyl Cellosolve Formal, although it will be understood that many othertypes of water miscible organic solvents can be used.

The invention produces new and improved results in the electroplating ofcadmium and makes it possible to obtain very bright cadmium plates overa wide range of current densities. The amounts of additional materialsincorporated into the cadmium electrolyte in accordance with theinvention, are so small that the expense of the operation is not greatlyincreased and the improved results with respect to brightness andcurrent density range more than justify the cost.

The invention is hereby claimed as follows:

1. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and an amine salt of an aldonic acid.

2. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte, an amine salt of an aldonic acid' and a nickel aldonate.

3. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and a nickel aldonate.

4. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and an arylamine salt of gluconic acid.

5. An aqueous cyanide-cadmium plating bath comprising acyanide-cadmium-electrolyte, an arylamine salt of gluconic acid andnickel gluconate.

6. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and nickel gluconate.

7. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and alpha naphthlyamine gluconate.

8. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte, alpha naphthylamine gluconate and nickel gluconate.

9. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte and alpha naphthylamine gluconate in proportions within therange of about 0.25 gram to 1 gram per gallon of the plating bath.

10. An aqueous cyanide-cadmium plating bath comprising a cyanide-cadmiumelectrolyte, about 1 gram per gallon of alpha naphthylamine gluconateand about 7 cc. per gallon of nickel gluconate solution with the amountof nickel per liter of nickel gluconate solution corresponding to about24 grams.

11. A brightener solution for cyanide-cadmium electrolytes comprising anamine salt of an aldonic acid and a nickel salt of an aldonic acid.

12. A brightener solution for cyanide-cadmium electrolytes comprising anarylamine gluconate and nickel gluconate, said solution serving toincrease the brightness of the electrodeposited cadmium and to extendthe range of current densities over which bright deposits are obtained.

13. A brightener solution for cyanide-cadmium electrolytes comprisingalpha naphthylamine gluconate and nickel gluconate, said solution, whenadded in small amounts to a cyanide-cadmium electrolyte, serving toincrease the brightness of the electrodeposited cadmium and to extendthe range of efiective current densities.

14. A brightener solution for cyanide-cadmium electrolytes comprising anamine salt of an aldonic acid, a nickel salt of an aldonic acid, a watermiscible organic solvent for said salts, and a substantial proportion ofa cadmium electrolyte.

15. A solution for addition to cyanide-cadmium plating baths to improvethe plating characteristics thereof, particularly with respect tobrightness and effective current densities range, said solutioncomprising approximately 2 grams alpha naphthylamine gluconate 15 cc.nickel gluconate containing about 24 grams per liter of nickel 50 cc. ofa cyanide-cadmium electrolyte 50 cc. diethyleneglycolmonobutylether,

said solution producing marked increase in brightness ofelectrodeposited cadmium when added to a cyanide-cadmium electrolyte inproportions within the range of to 5'7 cc. of solution per gallon ofelectrolyte and also serving to extend the effective current densityrange of said electrolyte.

16. In the electrodeposition of cadmium, the step which compriseselectrodepositing cadmium from an aqueous cyanide-cadmium plating bathhaving dissolved therein an amine salt of an aldonic acid.

1'7. In the electrodeposition of cadmium, the step which compriseselectrodepositing cadmium from an aqueous cyanide-cadmium plating bathhaving dissolved therein an amine salt of an aldonic acid and a nickelsalt of an aldonic acid.

18. In the method of electrodepositing cadmium, the step which compriseselectrodepositing cadmium from an aqueous cyanide-cadmium plating bathhaving dissolved therein a nickel salt of an aldonic acid.

19. In the electrodeposition of cadium, the step which compriseselectrodepositing cadmium from an aqueous cyanide-cadmium plating bathhaving dissolved therein an aromatic amine gluconate and nickelgluconate.

20. In the electrodeposition of cadmium. the step which compriseselectrodepositing cadmium from an aqueous cyanide-cadmium plating bathhaving dissolved therein alpha naphthylamine gluconate and nickelgluconate.

ALLAN E. CHESTER. FREDERICK F. REISINGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Modern Electroplating (1942), p.104, published by the American Electrochemical Society.

